Index: compiler-rt/lib/msan/msan_interceptors.cpp
===================================================================
--- compiler-rt/lib/msan/msan_interceptors.cpp
+++ compiler-rt/lib/msan/msan_interceptors.cpp
@@ -310,9 +310,23 @@
   CopyShadowAndOrigin(dest, src, n + 1, &stack);
   return res;
 }
-#define MSAN_MAYBE_INTERCEPT_STPCPY INTERCEPT_FUNCTION(stpcpy)
+
+INTERCEPTOR(char *, stpncpy, char *dest, const char *src, SIZE_T n) {
+  ENSURE_MSAN_INITED();
+  GET_STORE_STACK_TRACE;
+  SIZE_T copy_size = internal_strnlen(src, n);
+  if (copy_size < n)
+    copy_size++;  // trailing \0
+  char *res = REAL(stpncpy)(dest, src, n);
+  CopyShadowAndOrigin(dest, src, copy_size, &stack);
+  __msan_unpoison(dest + copy_size, n - copy_size);
+  return res;
+}
+#  define MSAN_MAYBE_INTERCEPT_STPCPY INTERCEPT_FUNCTION(stpcpy)
+#  define MSAN_MAYBE_INTERCEPT_STPNCPY INTERCEPT_FUNCTION(stpncpy)
 #else
 #define MSAN_MAYBE_INTERCEPT_STPCPY
+#  define MSAN_MAYBE_INTERCEPT_STPNCPY
 #endif
 
 INTERCEPTOR(char *, strdup, char *src) {
@@ -1686,6 +1700,7 @@
   INTERCEPT_FUNCTION(wmemmove);
   INTERCEPT_FUNCTION(strcpy);
   MSAN_MAYBE_INTERCEPT_STPCPY;
+  MSAN_MAYBE_INTERCEPT_STPNCPY;
   INTERCEPT_FUNCTION(strdup);
   MSAN_MAYBE_INTERCEPT___STRDUP;
   INTERCEPT_FUNCTION(strncpy);
Index: compiler-rt/lib/msan/tests/msan_test.cpp
===================================================================
--- compiler-rt/lib/msan/tests/msan_test.cpp
+++ compiler-rt/lib/msan/tests/msan_test.cpp
@@ -1687,6 +1687,21 @@
   EXPECT_NOT_POISONED(y[2]);
 }
 
+TEST(MemorySanitizer, stpncpy) {
+  char *x = new char[3];
+  char *y = new char[5];
+  x[0] = 'a';
+  x[1] = *GetPoisoned<char>(1, 1);
+  x[2] = '\0';
+  char *res = stpncpy(y, x, 4);
+  ASSERT_EQ(res, y + 2);
+  EXPECT_NOT_POISONED(y[0]);
+  EXPECT_POISONED(y[1]);
+  EXPECT_NOT_POISONED(y[2]);
+  EXPECT_NOT_POISONED(y[3]);
+  EXPECT_POISONED(y[4]);
+}
+
 TEST(MemorySanitizer, strcat) {
   char a[10];
   char b[] = "def";